Application of low dose of fludarabine and cyclophosphamide combined with donor NK Cells as a non-myeloablative conditioning regimen for the haploidentical hematopoietic stem cell transplantation in mice

This study was aimed to investigate the feasibity of low dose of fludarabine, cyclophosphamide combined with donor derived alloreactive NK cells as a new nonmyeloablative conditioning regimen in the haploidentical hematopoietic stem cell transplantation (haploidentical HSCT). F1 derived-NK cells were enriched with MACS magnetic separation system, in which the proportions of the Ly49C+ and Ly49A+ cells were detected by flow cytometry and the alloreactivity was measured by LDH method. The haploidentical HSCT models were constructed, and the myeloablativity in vivo, donor engraftment and the intensity of GVHD were compared between different myeloablative and nonmyeloablative conditioning regimens, including 9 Gy TBI, 6.5 Gy TBI, flu+cy, and flu+cy+allo-NK. The results showed that the flu+cy+allo-NK conditioning was nonmyeloablative, but the rate of donor chimerism after haploidentical HSCT was significantly higher as compared with other nonmyeloablative methods, which were (28.70±5.90)% in bone marrow and (46.40±5.00)% in spleen at day 21 post-transplantation. When compared with the flu+cy conditioning, the intensity of GVHD was slight in the flu+cy+allo-NK group, in which only a half of C57BL/6 recipients experienced weight loss, and no distinct pathological damages observed in the liver, intestine, kidney and skin samples. It is concluded donor derived-alloreactive NK cells can facilitate engraftment of the haploidentical hematopoietic stem cells and mitigate GVHD. The flu+cy+allo-NK conditioning provides a new method for those elder patients with high-risk solid tumor undergoing haploidentical-HSCT.